Turbulent jet ignition (TJI) engines utilize a pre-chamber to combust a small fraction (e.g., ˜3%) of a total fuel amount/energy for a cylinder combustion event. This small fuel charge is rich and a conventional spark plug is typically used for its ignition. A high-pressure jet stream of hot gasses resulting from the combustion is forced through a plurality of small orifices in the pre-chamber and into a main injection chamber of the cylinder. These hot gasses cause ignition of a primary charge of air/fuel mixture within the main combustion chamber without using a spark. For example, these orifices could be designed to optimize the spray of the hot gasses to achieve a more even burn within the main combustion chamber. While a rich fuel pre-charge is required, the main air/fuel charge is able to be much leaner than stoichiometric, which results in improved engine efficiency.
Conventional TJI engine fuel control systems inject liquid fuel into the pre-chamber. One problem with this strategy, however, is that liquid fuel may not be ignitable in the pre-chamber at certain operating conditions, such as engine cold starts and light load conditions. More specifically, fuel vaporization does not occur at these operating conditions, which is necessary to be able to ignite the fuel in the pre-chamber. The failure to ignite the fuel in the pre-chamber could cause increased engine emissions. Providing additional fuel could also increase emissions and/or decrease fuel economy. Accordingly, while such TJI fuel control systems work well for their intended purpose, there remains a need for improvement in the relevant art.